Learning to write is onerous and takes several years to master. It is particularly taxing for children with dyslexia and/or developmental coordination disorder (DCD) who appear to have difficulties with spelling and handwriting skills which are critical for writing development. Yet, little is known about the nature of these difficulties. A complicating factor to understanding the nature of spelling and handwriting impairments in dyslexia and DCD is the reported frequent comorbidity and the unclear relationship between the two disorders.
The programmatic set of studies presented in this thesis aimed first to understand the relationship between dyslexia and DCD and the comorbidity between the two and secondly to understand the nature of spelling and handwriting impairments in dyslexia and DCD. To address these aims, the prevalence and cognitive, motor, and literacy profiles of dyslexia, DCD, and comorbid dyslexia and DCD was examined in detail. Then, the nature of
handwriting difficulties in dyslexia and/or DCD was elucidated by probing profiles and correlates of handwriting in the context of fluency, legibility, and learning to form new letterlike characters.
The results demonstrated that dyslexia and DCD have independent and shared
impairments and are frequently comorbid with one another. The patterns of these impairments as well as the nature of comorbidity between the two highlights the multifactorial nature of the disorders. The multifactorial nature of dyslexia and DCD also manifested in their multifaceted handwriting difficulties. Handwriting difficulties in dyslexia and DCD were apparent as dissociable impairments which reflected the nature of the specific disorder as well as impairments in early acquisition of handwriting related motor knowledge.
These findings are considered in relation to implications for identification and remediation of handwriting difficulties and comorbid dyslexia and DCD.